Land managers wishing to monitor the groundwater on their property have recognized the advantages of being able to divide a single borehole into a number of zones to allow monitoring of groundwater in each of those zones. If each zone is sealed from an adjacent zone, an accurate picture of the groundwater can be obtained at many levels without having to drill a number of boreholes that each have a different depth. A groundwater monitoring system capable of dividing a single borehole into a number of zones is disclosed in U.S. Pat. No. 4,204,426 (hereinafter the '426 patent). The monitoring system disclosed in the '426 patent is constructed of a plurality of casings that may be connected together in a casing assembly and inserted into a well or borehole. Some of the casings may be surrounded by a packer element made of a suitably elastic or stretchable material. The packer element may be inflated with fluid (gas or liquid) or other material to fill the annular void between the casing and the inner surface of the borehole. In this manner, a borehole can be selectively divided into a number of different zones by appropriate placement of the packers at different locations in the casing assembly. Inflating each packer isolates zones in the borehole between adjacent packers.
The casings in a casing assembly may be connected with a variety of different types of couplers. One type of coupler that allows measurement of the quality of the liquid or gas in a particular zone is a coupler containing a valve measurement port (hereinafter the measurement port coupler). The valve can be opened from the inside of the coupler, allowing liquid or gas to be sampled from the zone surrounding the casing.
To perform sampling, a special measuring instrument or sample-taking probe is provided that can be moved up and down within the interior of the casing assembly. The probe may be lowered within the casing assembly on a cable to a known point near a measurement port coupler. As disclosed in the '426 patent, when the probe nears the location of the measurement port coupler, a location arm contained within the probe is extended. The location arm is caught by a helical shoulder that extends around the interior of the measurement port coupler. The location arm slides down the helical shoulder, rotating the sample-taking probe as the probe is lowered. At the bottom of the helical shoulder, the location arm reaches a stop that halts the downward movement and circumferential rotation of the probe. When the location arm stops the probe, the probe is in an orientation such that a port on the probe is directly adjacent to, and aligned with, the measurement port contained in the measurement port coupler.
When the probe is adjacent the measurement port, a shoe is extended from the sample-taking probe to push the probe in a lateral direction within the casing. As the shoe is fully extended, the port in the probe is brought into contact with the measurement port in the measurement port coupler. At the same time that the probe is being pushed against the measurement port, the valve within the measurement port is being opened. Simultaneously, with the movement of the measurement port valve, a hydraulic seal is made around the measurement port to connect the port on the probe with the fluid outside the measurement port coupler. The probe may therefore sample the gas or liquid contained in the zone located outside of the measurement port coupler. Depending upon the particular instruments contained within the probe, the probe may measure different characteristics of the exterior gas or liquid in the zone being monitored such as the pressure, temperature, or chemical composition. The probe may also allow samples of gas or liquid from the zone immediately outside the casing to be stored and returned to the surface for analysis.
After the sampling is complete, the location arm and the shoe lever of the probe may be withdrawn, and the probe retrieved from the casing assembly. It will be appreciated that the probe may be raised and lowered to a variety of different zones within the casing assembly, in order to take samples at each of the zones. A land manager may select the type of probe and the number and location of the zones within a borehole to configure a groundwater monitoring system for a particular application. The expandability and flexibility of the disclosed groundwater monitoring system therefore offers a tremendous advantage over prior art methods requiring the drilling of multiple sampling wells.
Currently, packer inflation and deflation are typically accomplished by attaching all of the packers in series to a single fluid line with fluid dispensed from a surface location. Each packer is attached to the single fluid line with a spring-biased valve. The spring tension of each valve is the same so that passage of fluid of a predetermined pressure through the single fluid line will open all of the valves and cause the simultaneous inflation of all of the packers. The above packer inflation system suffers from several disadvantages, all associated with the fact that the same pressure is applied to all of the packers. Applying the same pressure to all of the packers is undesirable in environments where packers located in different underground zones encounter different external pressures. In such an environment, the same packer pressure can result in some packers being overinflated and others underinflated. Additionally, different packers may have a slightly different resilience such that slightly greater or slightly less internal pressure may be necessary to expand a packer to a predetermined size. Again, the difference in resilience can result in packer overinflation or underinflation. Furthermore, the distance between the borehole and the below-ground casings is not entirely uniform throughout the length of the borehole. As a result, some packers must thus expand a greater distance from the casings than others in order to fill the void between the casings and the borehole. This is difficult to accomplish if variable packer inflation is not an option.
Minute variations in spring tension naturally occur in springs, and spring tension can change over time due to spring corrosion or fatigue. If the spring tension of all of the packer valves is not the same, some valves may not open to inflate a packer when other valves open. Spring-biased packer valves are sensitive to the fluid pressure inside the casing. For example, a high fluid pressure inside the casing could cause the valve to open and a high and destructive pressure to be applied to the interior of the expanding membrane of the packer, causing it to burst or otherwise fail. The use of spring-biased valves has another disadvantage. Specifically, spring-biased valves fail when the spring in a valve fails. Finally, the tension of the spring of a spring-biased valve imparts a minute pressure to pressure sensors, thus affecting pressure measurement accuracy, should it be desirable to know the packer inflation pressure.
In another method described in U.S. Pat. No. 4,230,180 (hereinafter the '180 patent), a probe is lowered to each packer and fluid is injected in packers one at a time. However, the '180 patent uses a spring-biased valve for each packer and, thus, has the same problems that are associated with spring-biased inflation valves, including the problem that spring-biased valves generally open to permit flow in one direction only. Therefore, such valves are not useful for deflating packers.
In order to solve the above-mentioned problems associated with a plurality of packers serially connected to a single inlet line, a separate fluid line for each packer has been used. The disadvantages associated with using a different fluid line for each packer include the redundancy of using multiple lines. Using multiple lines is more costly, occupies valuable casing space, and increases the likelihood of failure of one or more of the packers or lines. Also, there is typically a practical limit of about 6 to 12 lines that can be installed through adjacent packers, thereby limiting the number of packers that can be installed in a single borehole. However, there is frequently a need to install 20 to 40 or more packers in a single borehole. In such a case, the use of individual lines is impractical.
A need thus exists for a system for individually inflating and deflating an unlimited number of packers used to support a below-ground casing within a borehole that, preferably, avoids the use of spring-biased valves. The present invention is directed to fulfilling this need.